Empires usually involve slavery, which is horrible.
The Sumerians, Egyptians,Greeks, Romans, Turks, Arabs, British, French, Germans, Belgians, Portuguese, Spanish (and for all we know, the Aztecs and Incas etc) all had empires and enslaved people.
Apologies are meaningless - the facts need to be acknowledged and regretted but no-one alive today is to blame for the slavery of African people under the British and other empires (as a pp said, Africans themselves and Arab slave traders were culpable too in the trans-Atlantic trade).
Where does it end? Shall we ask Italy to send reparations for the Roman invasion and the 400 years of occupation, which must have involved slavery of the native Britons? Or the French for the Norman Conquest, after which lots of English peasants would have effectively been serfs or slaves? All nasty episodes in history.
I'm not sure how the huge emphasis on past slavery helps anyone really. It's always been known about - I was taught about the evils of the slave trade at primary and secondary school long ago. I don't understand what's new - are there really lots of people in this country who didn't know about it?
(When I worked in education, I used to wonder frequently about Black History Month. Do black children want to see endless images of their ancestors as slaves? There are plenty of more positive images of black people to focus on. Not suggesting suppression - I'm just putting my self in their place and wondering if it's the way I'd want to see myself represented so repeatedly. Also - Black History is History, isn't it? I don't like the 'ghetto-isation' - it's all history, surely.)